In frequency hopping type spread spectrum radio communication equipment, generally, a clock mainly used in an RF circuit section has significantly different frequency from that of a clock generally used in other base band processing circuits or a central processing unit (hereinafter generally referred to as CPU). For the RF circuit section, a high frequency RF clock signal is used. On the other hand, for the circuit section other than the RF circuit including a base band processing circuit, and a section for respective circuits of the CPU, an operation clock signal having lower frequency than the RF clock signal is used. This means that in the RF circuit section to be driven by a RF clock signal having higher frequency, more current is consumed than other circuit section.
In view of the foregoing, in order to suppress an overall current consumption of the entire circuit, the radio communication equipment is generally arranged such that a high frequency RF clock signal generated by an RF clock generating device is supplied only to the RF circuit section, and an operation clock signal having a frequency not as high as the RF clock signal, which is either obtained by dividing the frequency of the RF clock frequency generated by the RF clock generating device or generated by another operation clock generating device is supplied to the circuit section other than the RF circuit section.
Along with the rapid popularization of a battery-driven portable radio communication equipment, a method of periodically carrying out transmission and receiving and stopping the operation of the clock generating device in the period in which the transmission and receiving is not carried out is generally adopted in order to reduce the power consumption.
For example, Japanese Unexamined Patent Application Tokukai No. 2001-345732 (published on Dec. 14, 2001) discloses the structure wherein while an RF circuit section is being operated for transmitting and receiving, modulation and demodulation processes are carried out in a base band processing circuit by supplying a high speed clock signal from the side of the RF circuit; on the other hand, while transmission/receiving is not being carried out, it is waited for the next transmission/receiving start timing set by the timer section which receives a clock signal from a low speed clock generating circuit placed in other part than the RF circuit section. With this structure, the power consumption can be reduced in the state where the transmission and receiving is not being carried out by stopping the supply of a high speed clock to other sections than the timer section in the stand-by state.
According to the foregoing technique, the radio communication equipment can be arranged such that while the transmission and receiving is not being performed, only a timer section, a CPU, a memory, and a display device are operated, and operations in the base band processing circuit section other than the RF circuit section and the timer section are stopped, thereby reducing power consumption.
However, the foregoing conventional structure of reducing power consumption by performing transmission and receiving operations periodically, and stopping the supply of clocks to the RF circuit section and the most part of the base band processing circuit section while transmission and receiving operations are not being performed has the following problem. In the foregoing conventional technique, clocks are deviated between the transmitting side and the receiving side, or the clock is adjusted for the deviation, which may also lead to a shift in the next transmission/receiving restart timing to be waited by the timer section.
Further, the foregoing conventional technique merely enables a reduction in power consumption while transmission and receiving is not being performed by periodically carrying out transmission/receiving operations, and does not permit delicate adjustments, which can be effective for reducing the power consumption. Specifically, according to the foregoing technique, it is not possible to adjust the period of supplying a high speed clock according to an amount of data without disturbing the data communication, for example, when data communication is not performed in the transmission and receiving period, the supply of the high speed clock is stopped till the next transmission; on the other hand, when data communication has not been completed in the transmission/receiving period, the period of supplying the high speed clock is extended for a predetermined so that communication of all the data can be completed.
In the conventional technique, the operation of the CPU section which consumes more power as well as the RF circuit section and the base band processing circuit section is not stopped.